Root system development in Caucasian clover cv. Monaro and its contribution to seed yield

Abstract

A sand bed was used to investigate root system development and the relationship between the root system and seed yield of Caucasian clover (Trifolium ambiguum). During vegetative growth (September to November) root dry matter (DM) accumulated more rapidly than shoot DM, and the root to shoot ratio was 2.52 by mid November. However, as reproductive growth accelerated the rate of root DM accumulation decreased, and by early February the root to shoot ratio was 0.78. Plants developed primary, secondary, and tertiary crowns in this first growing season, with both primary and secondary crowns producing reproductive shoots. The protracted flowering period (five months) was a result of an initial production of reproductive shoots from primary crowns, and an extended production of reproductive shoots from secondary crowns when primary crown shoot production had ceased. A single primary crown produced an average seed yield of 3.8 g compared with 0.81 g seed from an average secondary crown. However, as there was only one primary crown but there were 26 secondary crowns per plant, the total seed yield from secondary crowns reached 21.1 g per plant. Seed yield per plant was, therefore, almost entirely dominated by the number and size of the secondary crowns. Root DM was highly correlated (R2 = 0.80–0.97) with the number of leaves, reproductive shoots, and inflorescences, as well as the number of secondary crowns, suggesting that the potential for seed production is strongly influenced by the size of the root system prior to reproductive development.